Piston



W. KRAMER 'Sept. 22, 1942.

PISTON Filed Nov. 27, 1939 w/z HELM mwihew,

Inventor.

Patented Sept. 22, 1942 PISTON Wilhelm Kramer, Neckarsulm, Wurttemberg,

Germany, asaignor to American Lm'gl Corporation, New York, N. Y., acorporation of New York Application November 27, 1939, Serial No.306,421 In Germany November 2, 1938 8 Claims.

The present invention relates to pistons, and particularly to pistonshaving oval elastic skirts. Pistons having oval elastic skirts have beenheretofore utilized in internal combustion engines. In such pistons, asa rule, the eyelets .in which the wrist pin is mounted have beenconnected by suitable ribs with the head and the annular part of thepiston below the head. When such a piston is heated, as it is by theexplosion of the fuel in the cylinder, the high temperature of thepiston head is transmitted to the skirt and the wrist pin eyelets anddeforms the skirt so that it becomes more or less circular in crosssection. In such pistons the skirt is usually separated partially fromthe piston head by a slot located in a plane transverse to the cylinderaxis. to permit such deformation.

A great disadvantage of the prior art has been that in pistons of thistype the deformation is so great that after high heating the skirt uponcooling does not resume its former ovel shape,

but retains a rounder shape. In other words, the

piston exceeds its elastic limits in the expansion and therefore itsskirt does not return to its oval form. Obviously this results in a poorfit of the skirt within the cylinder.

The problem is particularly grave in the case of light metal pistons.These metals are especially subject to the disadvantage of failing toreturn to their original shape upon cooling, when they have beendistorted by heat. In such pistons it has been found that the skirtcannot be properly supported and that the wrist pin eyelets are likelyto assume an inclined position and thus to give improper support to thewrist pin. This is even more true in the case of pistons in which a ribperpendicular to the piston head or parallel to the cylinder axis isprovided between the piston head and the eyelet for the wrist pin. Sucha construction deforms the skirt to a great extent and thus renders thepiston unsatisfactory.

The primary object of the present invention is to provide a piston whichin use does not undergo a permanent deformation from its original ovalform. It has been found that, if the amount of deformation is limited insome manner so that it does not exceed 50% of the normal deformation atpresent experienced, this deformation is sufficient when heated toprovide the necessary play in the engine cylinder, and at the same timeto avoid any permanent deformation so that upon cooling the pistonreturns to its original shape. This keew the'wrist pin in properposinates the rubbing of the lower portion of the skirt againts thecylinder walls which occurs if too great a deformation takes place.

A further object of the present invention is to provide a light metalpiston in which a special construction limits the deformation of theskirt and prevents deformation thereof beyond the elastic limit of thematerial.

A further object of the invention is to provide a light metal piston inwhich these results are accomplished by providing a connecting bar orstra across the piston, parallel to and close to the wrist pin, toconnect opposing sides of the skirt. This strap is so located that itreaches a temperature somewhere between those of the piston head and thepiston skirt. In such a manner the strap expands less than the head, sothat the expansion of the piston skirt is thereby limited.

The invention is preferably applied to a piston having an uninterruptedskirt, which is of course simple to manufacture since the cutting ofslots therein parallel to the cylinder axis is unnecessary. Also it isapplied preferably to a piston tion in the cylinder, and at the sametime elimiwhich in at least some of the planes through the cylinder axispresents a continuous surface. While slots may be provided in planestransverse to the cylinder axis, in the annular part of the pistonadjacent the cylinder head, these slots do not extend completely aroundthe piston, and particularly do not extend around the piston in theplane which contains the wrist pin axis.

Further objects and advantages of the invention will appear more fullyfrom the following description, particularly when taken in conjunctionwith the accompanying drawing which forms a part thereof.

Fig. 1 shows in cross section through the wrist pin axis a pistonembodying one form of the invention;

Fig. 2 is a cross section on the line IIII of Fig. 1;

Fig. 3 is a view similar to Fig. 1 of a modified form of the invention;

Fig. 4 is a cross section on the line IV-IV of Fig. 3.

The piston as shown in Figs. 1 and 2 includes a piston head 2 belowwhich is an annular portion 4. Downwardly extending from the annularportion 4 is the continuous skirt 6. The wrist pin receiving openings 8are provided in projections or bosses H) of the skirt. In order topermit deformation of the skirt when heated, there are provided in theannular portion 4 horizontal slots l2, these slots being located so thatthey ton is of course hollow, and is preferably formed of any well knownlight metal or light metal alloy.

In the form shown, as will be apparent from a careful inspection of thedrawing, the piston is of oval form, its dimension transverse to thewrist pin axis being slightly greater than its dimension parallel tothis axis. Fig. 2 clearly shows this difierence in dimensions whencompared with Fig. 1.

A piston so constructed would have the disadvantage that upon expansionof the parts thereof the skirt might expand in the direction of thearrows ll of Fig. 1, and thus change the oval shape of the piston to amore nearly circular shape. If this deformation exceeds a certainamount, the piston will not return to its normal oval shape upon beingcooled again. To avoid such great expansion, there is provided aconnecting strap l6 which extends across from one side of the piston tothe other, parallel to and just above the bosses ID of the wrist pinopenings. In the form shown in Figs. 1 and 2, this strap is integralwith the piston body. The strap is not heated as highly as the head,although it will be heated more than the skirt. It will thus limit theexpansion caused by the piston head. on the skirt, since it will holdthe skirt outwardly against the forces exerted by the highly heatedpiston head.

In some types of engines, as for instance in air cooled Diesel engines,the piston head is subjected to very great heat. Under these conditionsit may sometimes happen that the strap is will be inadequate to limitthe expansion of the skirt sufllciently, since it will be heated to sogreat a temperature that it will not prevent excess deformation of theskirt, even though its temperature may be less than that of the head.The form of the invention shown in Figs. 3 and 4 avoids even thisdisadvantage. In this case instead of utilizing a strap integral withthe head there is used a strap of a material having a lower coeflleientof expansion than the material of the piston body. In the case of lightmetal alloys, for example, this connecting member may be of steel.

The piston shown in Figs. 3 and 4 has a head, annular member, skirt andwrist pin bosses and openings similar to those of Figs. 1 and 2. Howeverit is provided just above the wrist pin bosses with openings havingcountersunk outer ends. Through these openings extends a tie member ortie rod l8, the ends of which are upset as at 20 in the countersunkopenings. This tie rod thus rigidly connects together the two sides ofthe piston, except as it may expand slightly when heated. Any othersuitable tie member might be used.

By carefully selecting the material of which such a tie rod is made,with a view to its particular coefficient of expansion, it is possibleto "utilize such a construction to control as desired the variations inthe shape of the skirt so as to obtain any desired effect.

While I have described herein some embodiments of my invention I wish itto be understood .that I do not intend to limit myself thereby exceptwithin the scope of the appended claims.

I claim: a

engines comprising a head, an annular part extending from said head, anda skirt of oval cross section extending below said annular part. saidpiston having a slot therein located in a plane transverse to thelongitudinal axis of the piston between the annular portion and theskirt, said skirt having means to receive a wrist pin and means,symmetrical with respect to the longitudinal plane of the pistoncontaining the axis of the wrist pin receiving means, and parallel tothe axis of said wrist pin receiving means, connecting the oppositesides of said skirt, said last means comprising a strap of a materialhaving such a eoefiicient of expansion as to prevent deformation of theskirt beyond a predetermined amount when the piston is subjected to apredetermined temperature.

2. A light metal piston for internal combustion engines comprising ahead, an annular par-textending from said head, and a skirt of ovalcross section extending below said annular part, said piston having aslot therein located in a plane transverse to the longitudinal axis ofthe piston between the annular portion and the skirt, said skirt havingmeans to receive a wrist pin. and means, symmetrical with respect to thelongitudinal plane of the piston containing the axis of the wrist pinreceiving means, and above said wrist pin receiving means and extendingparallel to the axis thereof, connecting the opposite ides of saidskirt, said last means comprising a strap of a material having such acoeflicient of expansion as to prevent deformation of the skirt beyond apredetermined amount when the piston is subjected to a predeterminedtemperature.

3. A piston for internal combustion engines iormed of light metal andcomprising a head, an annular portion extending from said head, and askirt extending from said annular portion said skirt having wrist pinreceiving means, said annular portion and skirt being of greaterdiameter in a direction transverse to the axis of said wrist pinreceiving means than in a direction parallel to the axis of said wristpin receiving meansfla slot located in a plane transverse to thelongitudinal axis of the piston partially separating said annularportion from saidskirt, the piston skirt being circumferentiallyuninterrupted, and means, symmetrical with respect to the longitudinalplane of the piston containing the axis of the wrist pin receivingmeans, and extending parallel to the axis of said wrist pin receivingmeans, connecting the opposite sides of said skirt.

4. A piston for internal combustion engines formed of light metal andcomprising a head. an annular portion extending from .said head, and askirt extending from said annular portion. said skirt having wrist pinreceiving means, said annular portion and skirt being of greaterdiameter. in a direction transverse to the axis of said wrist pinreceiving means than in adirection parallel to the axis of said wristpin receiving means, a slot located in a plane transverse to thelongitudinal axis of the piston partially separating said annularportion from said skirt. the lateral face of said piston beingsubstantially uninterrupted in a plane including the axis of said wristpin receiving means, the piston skirt being circumferentiallyuninterrupted, and means,

.. symmetrical with respect to the longitudinal 1. A light metal pistonfor internal combustion 7 plane of the piston containing the axis of thewrist pin receiving means, and extending parallel to thefaxis of saidwrist pin receiving means, connecting the opposite sides of said skirt.

5. A piston for internal combustion engines formed of light metal andcomprising a head, an annular portion extending from said head, and askirt extending from said annular portion, said skirt having wrist pinreceiving means, said annular portion and skirt being of greaterdiameter in a direction transverse to the axis of said wrist pinreceiving means than in a direction parallel to the axis of said wristpin receiving means, a slot located in a plane transverse to thelongitudinal axis of the piston partially separating said annularportion from said skirt, the lateral face of said piston beingsubstantially uninterrupted in a plane including the axis of said;wristpin receiving means, the piston skirt being circumferentiallyuninterrupted, and means. symmetrical with respect to the longitudinalplane of the piston containing the axis of the wrist pin receivingmeans, and extending parallel to the axis of said wrist pin receivingmeans, and located thereabove connecting the opposite sides of saidskirt.

6. A piston for'internal combustion engines formed of light metal andcomprising a head, an annular portion extending from said head, and a.skirt extending from said annular portion, said skirt having wrist pinreceiving means, said annular portion and skirt being of greaterdiameter in a direction transverse to the axis of said wrist pinreceiving means than in a direction parallel to the axis of said wristpin receiving means, a slot located in a plane transverse to thelongitudinal axis of the piston partially separating said annularport-ion from said skirt, and means, symmetrical with respect to thelongitudinal plane of the piston containing the axis of the wrist pinreceiving means, and extending parallel to the axis of said wrist pinreceiving means, connecting the opposite sides of said skirt, said lastmeans comprising a member formed of a material having a differentcoeificient of expansion from the light metal of the piston.

'7. A piston for internal combustion engines formed of light metal andcomprising a head, an annular portion extending from said head, and askirt extending from said annular portion, said skirt having wrist pinreceiving means, said annular portion and skirt being of greater theaxis of said wrist pin receiving means, the piston skirt beingcirciumferentially uninterrupted, and means, symmetrical with respect tothe longitudinal plane of the piston containing the axis of the wristpin receiving means, and extending parallel to the axis of said wristpin receiving means and located thereabove, cortnecting the oppositesides of said skirt, said last means comprising a member formed of amaterial having a difl'erent coeflicient of expansion from the lightmetal of the piston.

8. A piston for internal combustionengines formed of light metal andcomprising a head, an annular portion extending from said head, and askirt extending from said annular portion, said skirt having wrist pinreceiving means. said annular portion and skirt being of greaterdiameter in a direction transverse to the axis of said wrist pinreceiving means than in a direction parallel to the axis of said wristpin receiving means, a slot located in a plane transverse to thelongitudinal axis of the piston partially separating said annularportion from said skirt, the lateral face of said piston beingsubstantially uninterrupted in a plane including the axis of said wristpin receiving meas, the lpiston skirt being circumferentiallyuninterrupted, and means, symmetrical with respect to the longitudinalplane of the piston containing the axis of the wrist pin receivingmeans, and extending parallel to the axis of said wrist pin receivingmeans and located thereabove, connecting the opposite sides of saidskirt, said last mean comprising a member formed of a material having adifferent coeflicient of expansion from the light metal of the pistonsuch as to prevent deformation of the skirt beyond a predeterminedamount when the piston is subjected to a predetermined temperature.

W'ILHELM KRAMER.

